1. Field of the Invention
This invention relates to backup software for backing up data on a computer system. In particular, the invention relates to a system and method for resuming backup of a volume including a plurality of files after a first backup operation terminates before completion, e.g., terminates due to a failure.
2. Description of the Related Art
Computer systems often employ backup solutions to backup data in order to protect it against hardware failure or data corruption. Data may be stored in a volume on a computer system in the form of files. Backup techniques for backing up a volume generally operate to create a backup image including all the files in the volume. The backup image may be used to restore the volume to the computer system in the event that it becomes necessary to do so, e.g., if the storage device on which the volume is stored fails, if the volume becomes corrupted, or if a user or software application needs to access the volume as it existed at the time the backup image was created.
As the backup image for the volume is being created, other application programs executing on the computer system may continue to access the volume and may modify the files in the volume. As a result, the backup image may not represent the state of the volume at a single point in time. This may be a problem in some cases, e.g., because different files in the volume may be inconsistent with respect to each other.
Thus, in many applications it is desirable to create a backup image that represents the state of the volume at a single point in time. One technique to accomplish this is to create a copy-on-write (COW) snapshot of the volume and then backup the volume to a backup image using the snapshot.
In normal operation, the backup operation may create a complete backup image of the volume, e.g., a backup image that includes all the files of the volume. However, in some cases it is possible that the backup operation may terminate before backing up all of the files. In this case the backup image will be incomplete and will not represent the volume in its entirety.